The transmission of electrical power, data, and telephone communications beneath buildings is carried out through wires and cables installed inside conduit pipes. The pipes are often assembled into bundles known as “duct banks.” Duct banks consist of multiple sections of ducting arranged in a rectangular pattern and held in position by “templates.” The templates are generally flat rectangular spacers each having a pattern of holes through which the pipes are inserted.
Duct banks are typically assembled on site or transported to a construction site where they are installed. During installation each duct bank is loaded into a trench along a predetermined route. Each duct bank is then joined with other similar duct banks with couplings, sealed and encased in concrete.
In the prior art, duct banks are assembled on the job site either in the trench or above ground near the trench. Typically, a first set of workers holds a set of templates at a predetermined angle and at the correct spacing to position and hold the ducts in place. A second set of workers positions each pipe in a set of corresponding holes in the templates by sliding it through the holes. The process is labor-intensive, dangerous, and subject to frequent interruption during assembly in order to provide realignment of the templates and undo jamming of the pipes.
The prior art has attempted to solve some of these problems. For example, U.S. Pat. No. 3,606,395 to Salerno, et al. discloses a method and apparatus of laying underground cables using preformed conduit sections. The preformed conduit sections are rectangular blocks having four longitudinal holes forming conduit pipes. The preformed conduit sections are aligned end to end to form four continuous ducts. However, the block conduit sections in Salerno require excess material to surround each conduit in order to form the conduit section. This excess material requires additional raw materials, which increases manufacturing costs.
U.S. Pat. No. 3,711,127 to Raffa discloses a closure to arrange conduit members into a duct bank. The closure includes a horizontal base, upright side walls formed integrally with the base, longitudinal side walls, and upright members attached to the base having a generally rectangular shape adapted to align and support conduit members. The upright side walls have tapered sleeves sized to align and support the conduit members. The closure is sealed and filled with an inert gas to improve insulation and heat dissipation. However, Raffa requires the use of a housing to encase the duct bank and inert gas to fill the housing, thereby making the arrangement expensive to manufacture and assemble.
U.S. Pat. No. 5,605,419 to Reinert discloses a method for assembling and installing duct banks. The duct banks are assembled with upright plastic grids having apertures sized to axially receive conduits. The grids are spaced apart along the length of the conduits. Spacers are installed in groups of four, onto conduit members, one on each corner of the cross section of the duct bank. Wooden supports are placed across the conduits to support the duct bank. However, the method requires the duct bank to be assembled at the jobsite, which requires additional workers and exposes the workers to unnecessary dangers, thereby increasing installation costs.
The prior art fails to disclose or suggest a method and apparatus for prefabricating duct banks at the point of pipe extrusion. The prior art also fails to disclose an automated method of assembly of duct banks. Therefore, there is a need in the prior art for a method and apparatus for manufacturing and preassembling a duct bank that reduces time and labor costs and increases worker safety.